DESCRIPTION: Each year hundreds of millions of Dental restorations is performed, and an ever-increasing fraction of these restorations involve the use of photopolymerizable polymer composites. Unfortunately, these composites still suffer from problems associated with polymerization shrinkage, the long timeframe for polymerization, lack of toughness of the resin material, thermal expansion mismatch, moisture uptake by the sample following polymerization, the presence of extractable, unreacted monomer following cure, inhibition of the polymerization by oxygen, and a general lack of understanding of the polymerization process. The result of these problems is often the premature failure of composite restorations. In this research critical shortcomings are addressed by 1) developing novel monomer systems that will be more rapidly polymerizable, reach higher double bond conversions, improve the mechanical properties, and limit the effects of oxygen inhibition, 2) evaluating which aspects of the cure methodology are important in dictating how much polymerization shrinkage stress develops, and 3) developing a model that accurately predicts the polymerization kinetics as a function of temperature, initiation conditions (e.g., concentrations, light intensity, wavelengths), and composition. In addition to all of the property benefits, the success of this research in developing a more rapidly curing composite will improve the economics for the Dentist and, more importantly, will lead to improved compliance in the curing of thick restorations. It would be much simpler to fill a cavity in layers if each layer polymerizes significantly more rapidly than the current formulations. These results will combine to yield dramatically improved Dental composite systems.